Mems gyroscope

ABSTRACT

A MEMS gyroscope is disclosed herein, wherein the MEMS gyroscope comprises a movable portion capable of moving in response to angular velocity, a conducting wire attached to the movable portion for generating magnetic field, and a spintronic device for measuring the magnetic field. The conducting wire is disposed such that the current it carries is substantially perpendicular to the sensing direction of the sensing mode of the proof-mass.

CROSS-REFERENCE

This U.S. utility patent application claims priority from co-pendingU.S. utility patent application “A HYBRID MEMS DEVICE,” Ser. No.13/559,625 filed Jul. 27, 2012, which claims priority from U.S.provisional patent application “A HYBRID MEMS DEVICE,” tiled May 31,2012, Ser. No. 61/653,408 to Biao Zhang and Tao Ju. This US utilitypatent application also claims priority from co-pending U.S. utilitypatent application “A MEMS DEVICE,” Ser. No. 13/854,972 tiled Apr. 2,2013 to the same inventor of this U.S. utility patent application, thesubject matter of each of which is incorporated herein by reference inits entirety.

TECHNICAL FIELD OF THE DISCLOSURE

The technical field of the examples to be disclosed in the followingsections is related generally to the art of operation ofmicrostructures, and, more particularly, to operation of MEMS devicescomprising MEMS magnetic sensing structures.

BACKGROUND OF THE DISCLOSURE

Microstructures, such as microelectromechanical (hereafter MEMS) devices(e.g. accelerometers, DC relay and RF switches, optical cross connectsand optical switches, microlenses, reflectors and beam splitters,filters, oscillators and antenna system components, variable capacitorsand inductors, switched banks of filters, resonant comb-drives andresonant beams, and micromirror arrays for direct view and projectiondisplays) have many applications in basic signal transduction. Forexample, a MEMS gyroscope measures angular rate.

A gyroscope (hereafter “gyro” or “gyroscope”) is based on the Corioliseffect as diagrammatically illustrated in FIG. it. Proof-mass 100 ismoving with velocity V_(d). Under external angular velocity Ω, theCoriolis effect causes movement of the poof-mass (100) with velocityV_(s). With fixed V_(d), the external angular velocity can be measuredfrom V_(d). A typical example based on the theory shown in FIG. 1 iscapacitive MEMS gyroscope, as diagrammatically illustrated in FIG. 2,

The MEMS gyro is a typical capacitive MEMS gyro, which has been widelystudied. Regardless of various structural variations, the capacitiveMEMS gyro in FIG. 2 includes the very basic theory based on which allother variations are built. In this typical structure, capacitive MEMSgyro 102 is comprised of proof-mass 100, driving mode 104, and sensingmode 102. The driving mode (104) causes the proof-mass (100) to move ina predefined direction, and such movement is often in a form ofresonance vibration. Under external angular rotation, the proof-rnass(100) also moves along the V_(s) direction with velocity V_(s). Suchmovement of V_(s) is detected by the capacitor structure of the sensingmode (102). Both of the driving and sensing modes use capacitivestructures, whereas the capacitive structure of the driving mode changesthe overlaps of the capacitors, and the capacitive structure of thesensing mode changes the gaps of the capacitors.

Current capacitive MEMS gyros, however, are hard to achievesubmicro-g/rtHz because the capacitance between sensing electrodesdecreases with the miniaturization of the movable structure of thesensing element and the impact of the stray and parasitic capacitanceincrease at the same time, even with large and high aspect ratioproof-masses.

Therefore, what is desired is a MEMS device capable of sensing angularvelocities and methods of operating the same.

SUMMARY OF THE DISCLOSURE

In view of the foregoing, a MEMS gyroscope is disclosed herein, whereinthe gyroscope comprises: a first substrate, comprising: a movableportion that is capable of moving in response to an angular velocity; adriving mechanism associated with said movable portion for moving themovable portion along a driving direction in a driving mode; aconducting wire of a magnetic source on the movable portion forgenerating magnetic field; and a second substrate, comprising: amagnetic sensor that is a spintronic device for measuring the magneticfield from the conducting wire, wherein the magnetic sensor has an easyaxis and hard axis; wherein the hard axis is substantially parallel to asensing direction of a sensing mode of the movable portion; and whereinthe conducting wire is disposed such that the current it carries issubstantially perpendicular to the sensing direction of the sensing modeof the (proof-mass,

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 diagrammatically illustrates the Coriolis effect in a MEMSstructure;

FIG. 2 is a top view of a typical existing capacitive MEMS gyroscopehaving a driving mode and a sensing mode, wherein both of the drivingand sensing mode utilize capacitance structures;

FIG. 3 illustrates an exemplary MEMS gyroscope having a magnetic sensingmechanism;

FIG. 4 illustrates a top view of a portion of an exemplaryimplementation of the MEMS gyroscope illustrated in FIG. 3, wherein theMEMS gyroscope illustrated in FIG. 4 having a capacitive driving modeand a magnetic sensing mechanism;

FIG. 5 illustrates a perspective view of a portion of another exemplaryimplementation of the MEMS gyroscope illustrated in FIG. 3, wherein theMEMS gyroscope illustrated in FIG. 5 having a magnetic driving mechanismfor the driving mode and a magnetic sensing mechanism for the sensingmode

FIG. 6 illustrates an exemplary magnetic driving mechanism of the MEMSgyroscope in FIG. 5;

FIG. 7 illustrates an exemplary magnetic source of the MEMS gyroscopeillustrated in FIG. 3;

FIG. 8 illustrates an exemplary magnetic sensing mechanism that can beused in the MEMS gyroscope illustrated in FIG. 3;

FIG. 9 shows an exemplary thin-film stack that can be configured into aCIP or CPP structure for use in the magnetic sensing mechanismillustrated in FIG. 8;

FIG. 10 illustrates an exemplary MEMS gyroscope that comprises multiplemagnetic sensing structures;

FIG. 11 illustrates an exemplary MEMS gyroscope that comprises multipleproof-masses;

FIG. 12 illustrates an exemplary MEMS gyroscope that comprises multipleproof-masses having magnetic driving mechanisms;

FIG. 13a and FIG. 13b illustrate an exemplary driving scheme for use inthe MEMS gyroscope illustrated in FIG. 12;

FIG. 14 illustrates an exemplary magnetic source and magnetic sensingmechanism of the MEMS gyroscope illustrated in FIG. 13;

FIG. 15 illustrates another exemplary MEMS gyroscope that comprisesmultiple proof-masses having capacitive driving mechanisms;

FIG. 16a to FIG. 16d illustrate yet another exemplary MEMS gyroscopecomprising multiple proof-masses and multiple magnetic sources in atleast one of the proof-masses; and

FIG. 17 illustrates yet another exemplary MEMS gyroscope comprisingmultiple proof-masses, multiple magnetic sources in at least one of theproof-masses, and a reference magnetic sensor for the multiple magneticsensors.

DETAILED DESCRIPTION OF SELECTED EXAMPLES

Disclosed herein is a MEMS gyroscope for sensing an angular velocity,wherein the MEMS gyroscope utilizes a magnetic sensing mechanism. Itwill be appreciated by those skilled in the art that the followingdiscussion is for demonstration purposes, and should not be interpretedas a limitation. Many other variations within the scope of the followingdisclosure are also applicable. For example, the MEMS gyroscope and themethod disclosed in the following are applicable for use inaccelerometers.

Referring to FIG. 3, an exemplary MEMS gyroscope is illustrated herein,In this example, MEMS gyroscope 106 comprises magnetic sensing mechanism114 for sensing the target angular velocity through the measurement ofproof-mass 112, Specifically, MEMS gyroscope 106 comprisesmass-substrate 108 and sensor substrate 110. Mass-substrate 108comprises proof-mass 112 that is capable of responding to an angularvelocity, The two substrates (108 and 110) are spaced apart, forexample, by a pillar (not shown herein for simplicity) such that atleast the proof-mass (112) is movable in response to an angular velocityunder the Coriolis effect. The movement of the proof-mass (112) and thusthe target angular velocity can be measured by magnetic sensingmechanism 114.

The magnetic sensing mechanism (114) in this example comprises amagnetic source 116 and magnetic sensor 118. The magnetic source (116)generates a magnetic field, and the magnetic sensor (118) detects themagnetic field and/or the magnetic field variations that is generated bythe magnetic source (116). In the example illustrated herein in RUG. 3,the magnetic source is placed on/in the proof-mass (112) and moves withthe proof-mass (112), The magnetic sensor (118) is placed on/in thesensor substrate (120) and non-movable relative to the moving proof-mass(112) and the magnetic source (116). With this configuration, themovement of the proof-mass 12) can be measured from the measurement ofthe magnetic field from the magnetic source (116).

Other than placing the magnetic source on/in the movable proof-mass(1112), the magnetic source (116) can be placed on in the sensorsubstrate (120); and the magnetic sensor (118) can be placed on/ in theproof-mass (112).

It is also noted that the MEMS gyroscope illustrated in FIG. 3 can alsobe used as an accelerometer.

The MEMS gyroscope as discussed above with reference to FIG. 3 can beimplemented in many ways, one of which is illustrated in FIG. 4.Referring to FIG. 4, the proof-mass (120) is driven by capacitive, such.as capacitive comb. The sensing mode, however, is performed using themagnetic sensing mechanism illustrated in FIG. 3. For this reason,capacitive combs can be absent from the proof-mass (120).

Alternatively, the proof-mass can be driven by magnetic force, anexample of which is illustrated in FIG. 5. Referring to FIG. 5, the masssubstrate (108) comprises a movable proof-mass (126) that is supportedby flexible structures such as flexures 128, 129, and 130. The layout ofthe flexures enables the proof-mass to move in a plane substantiallyparallel to the major planes of mass substrate 108. In particular, theflexures enables the proof-mass to move along the length. and the width.directions, wherein the length direction can. be the driving modedirection and the width direction can be the sensing mode direction ofthe MEMS gyro device. The proof-mass (126) is connected to frame 132through flexures (128, 129, and 130). The frame (132) is anchored bynon-movable structures such as pillar 134. The mass-substrate (108) andsensing substrate 110 are spaced apart by the pillar (134). Theproof-mass (112.) in this example is driving by a magnetic drivingmechanism (136). Specifically, the proof-mass (126) can move (e.g.vibrate) in the driving mode under magnetic force applied by magneticdriving mechanism 136, which is better illustrated in FIG. 6.

Referring to FIG. 6, the magnetic driving mechanism 136 comprise amagnet core 138 surrounded by coil 140. By applying an alternatingcurrent through coil 140, an alternating magnetic field can be generatedfrom the coil 140. The alternating magnetic field applies magnetic forceto the magnet core 140 so as to move the magnet core. The magnet corethus moves the proof-mass.

The magnetic source (114) of the MEMS gyroscope (106) illustrated inFIG. 3 can be implemented in many ways, one of which is illustrated inFIG. 7. Referring to FIG. 7, conductive wire 142 is displaced on/inproof-mass 112. In one example, conductive wire 142 can be placed on thelower surface of the proof-mass (112), wherein the lower surface isfacing the magnetic sensors (118 in FIG. 3) on the sensor substrate(110, in FIG. 3). Alternatively, the conductive wire (142) can be placedon the top surface of the proof-mass (112), i.e. on the opposite side ofthe proof-mass (112) in view of the magnetic sensor (118). In anotherexample, the conductive wire (142) can be placed inside the proof-mass,e.g. laminated or embedded inside the proof-mass (112), which will notbe detailed herein as those examples are obvious to those skilled in theart of the related technical field.

The conductive wire (142) can be implemented in many suitable ways, oneof which is illustrated in FIG, 7. In this example, the conductive wire(142) comprises a center conductive segment 146 and tapered contacts 144and 148 that extend the central conductive segment to terminals, throughthe terminals of which current can be driven through the centralsegment. The conductive wire (142.) may have other configurations. Forexample, the contact tapered contacts (144 and 148) and the centralsegment (146) maybe U-shaped such that the tapered contacts may besubstantially parallel but are substantially perpendicular to thecentral segment, which is not shown for its obviousness.

The magnetic sensor 18) illustrated in FIG. 3 can be implemented tocomprise a reference sensor (150) and a signal sensor (152) asillustrated in FIG. 8. Referring to FIG. 8, magnetic senor 118 on/insensor substrate 120 comprises reference sensor 150 and signal sensor152. The reference sensor (150) can be designated for dynamicallymeasuring the magnetic signal background in which the target magneticsignal (e.g. the magnetic field from the conductive wire 146 asillustrated in FIG. 7) co-exists. The signal sensor (152) can bedesignated for dynamically measuring the target magnetic signal (e.g.the magnetic field from the conductive wire 146 as illustrated in FIG.7). In other examples, the signal sensor (152) can he designated fordynamically measuring the magnetic signal background in which the targetmagnetic signal (e.g. the magnetic field from the conductive wire 146 asillustrated in FIG. 7) co-exists, while the signal sensor (150) can bedesignated for dynamically measuring the target magnetic signal (e.g.the magnetic field from the conductive wire 146 as illustrated in FIG.7).

The reference sensor (150) and the signal sensor (152) preferablycomprise magneto-resistors, such as AMRs, giant-magneto-resistors (suchas spin-valves, hereafter SV), or tunneling-magneto-resistors (TMR). Fordemonstration purpose, FIG. 9 illustrates a magneto-resistor structure,which can be configured into CIP (current-in-plane, such as aspin-valve) or a CPP (current-perpendicular-to-plane, such as TMRstructure), As illustrated in FIG. 9, the magneto-resistor stackcomprises top pin-layer 154, free-layer 156, spacer 158, reference layer160, bottom pin layer 162, and substrate 120. Top pin layer 154 isprovided for magnetically pinning free layer 156. The top pin layer canbe comprised of IrMn, PtMn nr other suitable magnetic materials. Thefree layer (156) can be comprised of a ferromagnetic material, such asNiFe, CoFe, CoFeB, or other suitable materials or the combinationsthereof. The spacer (158) can be comprised of a non-magnetic conductivematerial, such as Cu, or an oxide material, such as Al₂O₃ or MgO orother suitable materials. The reference layer (160) can be comprised ofa ferromagnetic magnetic material, such as NiFe, CoFe, CoFeB, or othermaterials or the combinations thereof. The bottom pin layer (162) isprovided for magnetic pinning the reference layer (160), which can becomprised of a IrMn, PtMn or other suitable materials or thecombinations thereof The substrate (120) can be comprised of anysuitable materials, such as glass, silicon, or other materials or thecombinations thereof.

In examples wherein the spacer (158) is comprised of a non-magneticconductive layer, such as Cu, the magneto-resistor (118) stack can beconfigured into a CIP structure (i.e. spin-valve, SV), wherein thecurrent is driven in the plane of the stack layers. When the spacer 58)is comprised of an oxide such as Al₂O₃, MgO or the like, themagneto-resistor stack (118) can be configured into a CPP structure(i.e. TMR), wherein the current is driven perpendicularly to the stacklayers.

In the example as illustrated in FIG. 9, the free layer (156) ismagnetically pinned by the top pin layer (154), and the reference layer(160) is also magnetically pinned by bottom pin layer 162. The top pinlayer (15.4) and the bottom pin layer (162) preferably having differentblocking temperatures. In this specification, a blocking temperature isreferred to as the temperature, above which the magnetic pin layer ismagnetically decoupled with the associated pinned magnetic layer. Forexample, the top pin layer (154) is magnetically decoupled with the freelayer (156) above the blocking temperature T_(B) of the top pin layer(154) such that the free layer (156) is “freed” from the magneticpinning of top pin layer (154). Equal to or below the blockingtemperature T_(B) of the top pin layer (154), the free layer (156) ismagnetically pinned by the top pin layer (154) such that the magneticorientation of the free layer (156) is substantially not affected by theexternal magnetic field. Similarly, the bottom pin layer (162) ismagnetically decoupled with the reference layer (160) above the blockingtemperature T_(B) of the bottom pin layer (162) such that the referencelayer (160) is “freed” from the magnetic pinning of bottom pin layer(162). Equal to or below the blocking temperature T_(B) of the bottompin layer 62), the reference layer (160) is magnetically pinned by thebottom pin layer (162) such that the magnetic orientation of thereference layer (162) is substantially not affected by the externalmagnetic field.

The top and bottom pin layers (154 and 162, respectively) preferablyhave different blocking temperatures. When the free layer (156 is“freed” from being pinned by the top pin layer (154), the referencelayer (160) preferably remains being pinned by the bottom pin layer(162). Alternatively, when the free layer (156) is still pinned by thetop pin layer (154), the reference layer (160) can be “freed” from beingpinned by the bottom pin layer (162). In the later example, thereference layer (160) can be used as a “sensing layer” for responding tothe external magnetic field such as the target magnetic field, while thefree layer (156) is used as a reference layer to provide a referencemagnetic orientation,

The different blocking temperatures can be accomplished by usingdifferent magnetic materials for the top pin layer (154) and bottom pinlayer (162). In one example, the top pin layer (154) can be comprised ofIrMn, while the bottom pin layer (162) can be comprised of PtMn, viceversa. In another example, both of the top and bottom pin layers (154and 162) may be comprised of the same material, such as IrMn or PtMn,but with different thicknesses such that they have different blockingtemperatures.

It is noted by those skilled in the art that the magneto-resistor stack(118) is configured into sensors for sensing magnetic signals. As such,the magnetic orientations of the free layer (156) and the referencelayer (160) are substantially perpendicular at the initial state. Otherlayers, such as protective layer Ta, seed layers for growing the stacklayers on substrate 120 can be provided. It is further noted that themagnetic stack layers (118) illustrated in FIG. 9 are what is oftenreferred to as “bottom pin” configuration in the field of art. In otherexamples, the stack can be configured into what is often referred as“top pinned” configuration in the field of art, which will not bedetailed herein.

in some applications, multiple magnetic sensing mechanisms can beprovided, an example of which is illustrated in FIG. 10. Referring toFIG. 10, magnetic sensing mechanisms 116 and 164 are provided furdetecting the movements of proof-mass 112. The multiple magnetic sensingmechanisms can be used for detecting the movements of proof-mass 112 indriving mode and sensing mode respectively. Alternatively, the multiplemagnetic sensing mechanisms 116 and 164 can be provided for detectingthe same modes (e.g. the driving mode and/or the sensing mode).

In operation, angular velocity in Z direction (perpendicular to thedriving and sensing direction) causes the motion of the proof-mass inthe sensing direction. However, acceleration in the sensing directionalso causes the motion of the proof-mass in the sensing direction. As aconsequence, motion of the proof-mass in the sensing direction is amixture of both of the angular velocity in the Z direction andacceleration in the sensing direction when both exist. The signalmeasured by the magnetic sensing mechanism is thus a mixture of thesignals associated with the proof-mass motion in both directions. Asolution to separate signals from the angular velocity in Z directionand acceleration in the sensing direction can be provision of multipleproof-masses, an example of which is illustrated in FIG. 11. It is notedthat the example illustrated in FIG. 11 having two proof-masses is onlyfor demonstration purposes. Other variations within the scope of thisdisclosure are also applicable. For example, more than two proof-masses,such as four or eight proof-masses can be provided in a MEMS gyroscope.

Referring to FIG. 11, proof-masses PM1 170 and PM2 172 are provided in aMEMS gyroscope, The proof-masses (170 and 172) are connected to anchor115 through flexures 111 and 113 such that the proof-masses are capableof moving in the driving and sensing directions. It is noted that theproof-masses 170 and 172) are associated with other mechanicalstructures to enable the motion of the proof-masses, and thosemechanical structures are not shown herein for simplicity. Drivingmechanisms 117 and 119 are provided for driving the proof-masses (170and 172) in their driving modes. The driving mechanisms may comprisecapacitors or magnetic driving mechanisms or other suitable structures.

To separate the angular velocity in the Z direction and acceleration inthe sensing direction, the proof-masses PM1 and PM2 move in oppositedirections along the driving directions. For example, the proof-massesPM1 and PM2 move at the same time toward anchor 115 or at the same time,away from anchor 115. Because the proof-masses PM1 and PM2 have oppositevelocities in the driving direction, they also move in oppositedirections in the sensing direction under the Coriolis force due toangular velocity in the Z direction. In existence of accelerate in thesensing direction, both of the proof-masses 170 and 172 move in the samedirection at the same time. By analyzing the moving directions of theproof-masses 170 and 172, signals caused by the angular velocity in theZ direction and acceleration in the sensing direction can be separated.

As an example, FIG. 12 illustrates the MEMS substrate of a MEMSgyroscope having multiple proof-masses and using magnetic drivingmechanism. Referring to FIG. 12, proof-masses 170 and 172 are formed inMEMS substrate 108. The proof-masses 170 and 172 are connected to andheld by anchor 115 through flexures. The proof-masses 170 and 172 eachare connected to a magnetic driving mechanism. For example, proof-mass170 is connected to movable coil 123 that moves with proof-mass 170.Movable coil 123 is coupled to static coil 121 that is affixed to anchor125 such that static coil 121 does not move relative to substrate 108when proof-masses 170 and 172 are moving,

By driving current in the coupled coils in selected directions, thecoils generate attractive and repel forces, as illustrated in FIG. 13aand FIG. 13b . Referring to FIG. 13 a, the direction of the currentthrough movable coil 123 can be fixed, for example counter-clockwise.When the current in static coil 121 has a clockwise direction, the coils121 and 123 generate attractive force. Because the static coil (121) isaffixed to anchor 125 and static, the movable coil (123) is movestowards the static coil (121) under the attractive force, and so doesthe proof-mass (170). When both of the current in the static coil (121)and movable coil (123) have counter-clockwise direction, as illustratedin FIG. 13 bc, the force between the two coils is repellent. The movablecoil (123), on does the proof-mass (170), moves away from the staticcoil (121) under the repellent force.

By changing the direction of the current in the static coil whitekeeping the current direction in the movable coil unchanged, theproof-mass (170) can be moved towards and away from the static coil(121). In other examples, the current direction of the static coil (121)can be unchanged during operation, while the direction of the current inthe movable coil (123) is varied. In another example, both of thedirections of the current in the static and movable loops can be variedduring operation to driving the movable loop, as well as the proof-mass,away and towards the anchor (125). In any examples, the frequency ofchanging the current direction can be equal or close to the resonatefrequency of the proof-mass in the driving direction, It is noted thatmultiple static and movable loop pairs can be provided for a proof-massto increase the driving efficiency, even though FIG. 4a shows two coilpairs.

Proof-mass 172 can be driving in the same way as proof-mass 170 by usingthe magnetic driving mechanism associated therewith. In order toseparate signal of the Z direction angular velocity from theacceleration in the sensing direction, proof-masses 170 and 172 aredriving in opposite directions in the sensing mode as discussed abovewith reference to FIG. 11, which will not be repeated herein.

For detecting the motion of the proof-masses (170 and 172), multiplemagnetic sensing mechanisms are provided, and example of which isillustrated in FIG. 14. Referring to FIG. 14, Proof-mass 170 is providedwith a conducting wire (174) as a magnetic field source for generatingmagnetic field. The conducting wire (174) can be formed at the bottomsurface of proof-mass 170 as discussed above with reference to FIG. 3,Associated with conducting wire 170 is magnetic sensor 176 for measuringthe magnetic field from conducting wire 174, The magnetic sensor (176)is formed on sensor substrate 110 as shown in FIG. 3. The magneticsensor 176 can be the same as magnetic sensor 118 as discussed abovewith reference to FIG. 3. It is noted that magnetic sensor 176, whencomprised of a solid-state spintronic structure, such as a spin-valve ormagnetic-tunnel-junction, can be offset from conducting wire 174 alongthe direction of the sensing mode. Specifically, the geometric center ofmagnetic sensor 176 is offset from the closest conducting wire passingby. Similar to that for proof-mass 170, proof-mass 172 is provided withconducting wire 178 and associated sensing mechanism 180, which will notbe repeated herein.

In yet another example, the MEMS gyroscope as discussed above withreference to FIG. 3 can have multiple proof-masses and capacitivedriving mechanisms, an example of which is illustrated in FIG. 15.Referring to FIG. 15, proof-masses 170 and 172 are provided. Theproof-masses are driven by capacitive combs. For example, proof-mass 170is connected to one set of capacitive plates of a capacitor comb; andthe other set of capacitor plates 10 are connected to anchor 127. Bychanging the voltage between the capacitive plates, electrostatic forcecan be generated, The electrostatic force drives proof-mass 170 to movein the driving direction.

Similar to proof-mass 170, proof-mass 172 is also connected to a set ofcapacitor plates; and the other set of capacitor plates of a capacitorcomb is connected to an anchor. By changing the voltages between theplates, proof-mass 172 can be moved under electrostatic force caused bythe variation of the voltage.

The same to that in magnetic driving scheme as discussed above withreference to FIG. 14, the capacitor combs associated with proof-masses170 and 172 are operated asynchronously such that proof-masses 170 and172 move in opposite directions along the driving direction. In responseto the same angular velocity in Z direction, proof-masses 170 and 172move in opposite directions along the sensing direction.

Regardless of driving mechanisms, a proof-mass of a MEMS gyroscope mayhave multiple magnetic sources, an example of which is illustrated inFIG. 16a . Referring to FIG. 16a , the MEMS gyroscope comprisesproof-masses 170 and 172. At least one of the proof-masses 170 and 172comprises multiple magnetic sources. For example, proof-mass 170 isattached thereto conducting wires 14, 24 and 16, each of which iscapable of generating magnetic field. The conducting wires can beserially connected as shown in FIG. 16a . Associated with eachconducting wire, a magnetic sensor is provided but on the sensorsubstrate, which is illustrated as blocks with dotted lines. Forexample, magnetic sensors 22, 20 and 18 are associated with and alignedto conducting wires 14, 24 and 16 separately. By placing the conductingwires with distances larger than the sensitivity of the magneticsensors, magnetic field signals from neighboring wires may not bemeasured by a magnetic sensor.

In operation, current is driven through conducting wires 14, 24 and 16.The current carrying wires generate magnetic field in their vicinities.The magnetic sensors measure the magnetic field from the associatedconducting wires. The multiple magnetic source configuration can be ofgreat value especially when multiple magnetic sensors are desired, suchas Wheatstone bridge configuration.

It is noted that the magnetic sensors (18, 20, and 22) are aligned tothe conducting wires 14, 24 and 16 in terms of the magnetic fieldgenerated by the conducting wires. Taking magnetic sensor 22 for exampleas illustrated in FIG. 16b , magnetic sensor 22, which can be aspin-valve or a magnetic-tunnel-junction (MTJ) or other spintronicdevices, has an (magnetic) easy axis along its length and (magnetic)hard axis along its width, wherein the easy and hard axes are oftenperpendicular. The easy axis of magnetic sensor 22 is substantiallyparallel to the driving direction (the direction of the driving mode);and the hard axis is substantially parallel to the sensing direction(direction of the sensing mode).

The conducting wire 14 is disposed such that the current it carriesflows along the direction of the driving mode. The direction of thecurrent is perpendicular to the hard axis of the magnetic sensor 22 thatis the sensing direction of the magnetic sensor 22. During operation,current flows through the conducting wire 14, and generates magneticfield. The magnetic field along the driving direction (the directionalong the driving mode) is substantially uniform especially when theconducting wire has a length that is much larger than the magneticsensor, which is illustrated in FIG. 16c , Because of this uniformity,the magnetic field is insensitive to the movement of the conducting wireand the proof-mass. As a consequence, measuring the movement of theproof-mass through the measurement of the magnetic field along thedriving direction is difficult.

The magnetic field from the conducting wire 145, however, has a muchhigher magnetic field gradient along the sensing direction, which isillustrated in FIG. 16d . Higher magnetic field gradient benefits highersensitivity of measuring the movement of the proof-mass through themeasurement of the magnetic field generated by the conducting wire.Therefore, it is preferred that the conducting wire is disposed relativeto the magnetic sensor and the proof-mass in a way such that, thecurrent in the conducting wire is substantially perpendicular to thehard axis (also the sensing direction) of the magnetic sensor, andsubstantially perpendicular to the sensing direction of the sensing modeof the proof-mass.

It will be appreciated by those skilled in the art that theconfiguration as discussed above with reference to FIG. 6b is alsoapplicable to other MEMS gyroscopes, such as MEMS gyroscopes having oneproof-mass, and MEMS gyroscopes having more than two proof-masses, whichwill not be detailed herein due to their obviousness.

In examples using spintronic magnetic sensors such as spin-valves ormagnetic-tunnel-junctions, a reference magnetic sensor is often providedfor providing reference signals. The measured magnetic signals frommagnetic sensors can be compared with the reference signals followed byamplification. In the example as shown in FIG. 16a , each magneticsensor (e.g. 22, 20, and 18) can be associated with a reference sensor.The reference sensors are often identical in terms of structures, butare isolated from external magnetic field by being covered by a magneticinsulation layer, such as a soft magnetic material. In yet anotherexample, a reference sensor can be provided for multiple magneticsensors associated with a proof-mass, as illustrated in FIG. 17.

Referring to FIG. 17, magnetic sensors 18, 20, and 22. are provided formeasuring magnetic field from magnetic sources 16, 24, and 14respectively. The magnetic sources 14, 24, and 16 are attached toproof-mass 170 for measuring movements of proof-mass 170. Referencesensor 26 is provided for magnetic sensors 18, 20, and 22, The referencesensor (26) is substantially the same as magnetic sensors 118, 20, and22, but is magnetically insulated by being covered with a magneticinsulation layer such that reference sensor 26 is not responsive toexternal magnetic field.

The measured magnetic signals from magnetic sensors 18, 20, and 22 arecompared with the output signal form the reference sensor (26), and theoutput of the comparison can be amplified. The reference sensor (26) canbe placed at any suitable location in the vicinity of the magneticsensors 18, 20, and 22. In the example as illustrated in FIG. 17, thereference sensor (26) can be placed in the vicinity of magnetic sensor(18). It is noted by those skilled in the art that even though areference sensor is provided for a proof-mass, such as proof-mass 170,other proof-masses, such as proof-mass 172 may or may not be providedwith a reference sensor.

It will be appreciated by those of skilled in the art that a new anduseful MEMS gyroscope has been described herein. In view of the manypossible embodiments, however, it should be recognized that theembodiments described herein with respect to the drawing figures aremeant to be illustrative only and should not be taken as limiting thescope of what is claimed. Those of skill in the art will recognize thatthe illustrated embodiments can be modified in arrangement and detail.Therefore, the devices and methods as described herein contemplate allsuch embodiments as may come within the scope of the following claimsand equivalents thereof. In the claims, only elements denoted by thewords “means for” are intended to be interpreted as means plus functionclaims under 35 U.S.C. §112, the sixth paragraph.

We claim:
 1. A MEMS gyroscope, comprising: a first substrate,comprising: a movable portion that is capable of moving in response toan angular velocity; a driving mechanism associated with said movableportion for moving the movable portion along a driving direction in adriving mode; a conducting wire of a magnetic source on the movableportion for generating magnetic field; and a second substrate,comprising: a magnetic sensor that is a spintronic device for measuringthe magnetic field from the conducting wire, wherein the magnetic sensorhas an easy axis and hard axis; wherein the hard axis is substantiallyparallel to a sensing direction of a sensing mode of the movableportion; and wherein the conducting wire is disposed such that thecurrent it carries is substantially perpendicular to the sensingdirection of the sensing mode of the proof-mass.
 2. The MEMS gyroscopeof claim 1, wherein the spintronic device comprises a spin-valve.
 3. TheMEMS gyroscope of claim 1, wherein the spintronic device comprises atunnel-magnetic-resistor.
 4. The MEMS gyroscope of claim 1, wherein thedriving mechanism comprises a group of capacitors.
 5. The MEMS gyroscopeof claim 1, wherein the driving mechanism comprises a magnetic drivingmechanism.